Generate models types for Operation Requests and Responses (#549)

* Refactor filterOperationParameters into utils

* Consume latest autorest

* do not include optional params in addOperations for now

* Support additional Schemas in getyTypeForSchema

* add missing comment

* Add return types to Operations

* Add Union types, Polymorphism, inheritance, ResponseTypes

* Remove callbakc parameter and its overrides

* Add missing types to Client and ClientContext files

* Support add-credentials flag

* Multiple fixes

* Assignment of constant Client parameters

* Fix pipeline and use serializedName for discriminator

README.md

@@ -26,8 +26,9 @@ More information about these can be found [here](https://github.com/Azure/autore
 3. Hook up plugins into the AutoRest pipeline DAG, e.g.
 
 ```yaml
+version: 3.0.6189
 use-extension:
-  "@autorest/modelerfour": "4.2.75"
+  "@autorest/modelerfour": "4.3.142"
 
 pipeline:
   typescript: # <- name of plugin